View Camera Focusing and the Scheimpflug Principle

[Cletus]

Okay, I actually did a search on this and couldn't find a satisfactory answer to this question. - have also consulted my books and it is unclear:

When focussing any view camera, and applying the Scheimpflug law, why doesn't the entire scene, if done correctly, come into perfect, sharp focus on the GG? Even with many, complex movements? As in, you have correctly set the plane of focus to correspond with the important areas of the subject, which happens to NOT be parallel to the film plane. I've always been told and it seems to be this way in practice too, that you first focus on the far, make your movements for the near, then refocus until you have "split the difference" between the near and far. Neither will be in perfect focus, then stop down to bring everything relatively sharp for the shot. It seems to me tha if movements are properly applied, everything should be sharp already, even at a fairly large aperture.

Which brings me to part two of this question: The Scheimpflug principle states that when the subject plane of [desired] focus, the lens plane (front standard) and the film plane (rear standard) are all allowed to form converging lines, then everything on the subject plane will be in focus. Or something to that effect.

Here's a somewhat simplified example of what I'm asking here: It seems to me that if, for instance, you wanted to focus on a vertical wall, with the camera slightly pointed upward, and you left the front standard at zero and applied a little back tilt, you'd then have your converging lines, the "SP" would be satisfied and the wall would be able to brought into perfectly sharp focus at, say, f5.6. The building might be a little distorted in this example, but should still have wall in sharp focus, right?

Why can't I seem to be ale to achieve this in practice? It seems to me that ANY TIME I have a little front std front tilt and rear standard back tilt, I should be satisfying the SP and be able to bring that part of scene into razor sharp focus?

Frankly, I don't use that many movements in the type of photography I do. I.e., point camera at flat wall of building, level and zero everything, and trip shutter. Like I would with any non view camera. I've been discouraged from working with movements much, because of my frustrating lack of understanding on this focus issue.

Thanks ahead for your collective wisdom and comments!

Phil aka "Cletus"

[Cletus]

Maybe this too complicated a question? Is this like asking "how do I use my camera"?

Maybe to simplify -

If movements are used correctly, shouldn't the entire plane of focus be tack sharp on the GG without stopping down to f90?

If there is front-forward tilt and rear-back tilt, isn't the requirement for the SP focus typically met?

[E. von Hoegh]

Maybe this too complicated a question? Is this like asking "how do I use my camera"?

Maybe to simplify -

If movements are used correctly, shouldn't the entire plane of focus be tack sharp on the GG without stopping down to f90?

If there is front-forward tilt and rear-back tilt, isn't the requirement for the SP focus typically met?

If you knew precisely where the plane of focus should be, and you moved the front and rear standards the correct amount to make the planes intersect, the plane of focus would fall on the GG perfectly, the first time, every time. Since none of these conditions obtain, you go back and forth, checking the GG with a loupe, until you get it where you want it. Simply tilting the front and back is not correct - the three planes must intersect.

If you are having to stop down to f;90, you aren't getting the Scheimpflug movements right. Put a map on the table top, set up the camera above and to one side of the table. You will find that you can have the entire frame filled with a part of the map, at about lifesize on the GG, and the map will be perfectly sharp at maximum aperture, the map being a 2 dimensional object. If your subject is 3 dimensional, you still have to stop down the get the parts outside the plane (which by definition is 2 dimensional) of focus.

[timparkin]

If you knew precisely where the plane of focus should be, and you moved the front and rear standards the correct amount to make the planes intersect, the plane of focus would fall on the GG perfectly, the first time, every time. Since none of these conditions obtain, you go back and forth, checking the GG with a loupe, until you get it where you want it. Simply tilting the front and back is not correct - the planes must intersect.

If you are having to stop down to f;90, you aren't getting the Scheimpflug movements right. Put a map on the table top, set up the camera above and to one side of the table. You will find that you can have the entire frame filled with a part of the map, at about lifesize on the GG, and the map will be perfectly sharp at maximum aperture, the map being a 2 dimensional object. If your subject is 3 dimensional, you still have to stop down the get the parts outside the plane (which by definition is 2 dimensional) of focus.

In your example, move to the side of the camere, about 10 ft away. Draw a line through the rear standard where the film plane is; draw a line through the front standard where the lens board is. Project these who lines downward until they meet.

If the point where these two lines meet isn't part of the wall then you'll never get your subject in focus (this presumes a non-telephoto lens for reasons I can't be bothered to go into).

If you want the wall in focus with the camera pointed slightly up, the lens board plane, the film plane and the wall should all converge somewhere some distance below ground level.

Tim

[E. von Hoegh]

http://en.wikipedia.org/wiki/Scheimpflug_principle

[mandoman7]

The Scheimpflug Principle is not a theory, its a useful tool. Sometimes I can get lost and confused under the dark cloth when I don't seem to be able to find the plane I'm looking for, but it always is grounding to move away and look to the side of the camera to see if the 3 planes converge in a reasonable way. Like many things, practice seems to work wonders.

[rdenney]

There are cameras that are designed to make it easy, but they depend on a subject that has an obvious desired focus plane. Few scenes have all the subjects you want sharp in a single plane. So you have to make a decision about what to include in the focus plane, and then adjust the movements to achieve that. Then, use depth of field to bring the remainder into acceptable sharpness. The depth of field will be a wedge-shaped zone that is narrower the closer the focus plane is to the camera, so the tilts must be more precisely adjusted for near objectives where depth of field is less.

For landscapes, where you are mostly trying to run the focus plane along the ground, you can focus on the near object and then tilt (with base tilts) outward to bring in the distant object. But you will still probably have to readjust several times as you zero in on getting the focus plane exactly where you want it. It is possible to get it right.

In the picture below, I applied a small amount of downward tilt and a bit of swing. I picked three points on the trunk of the tree to be in precise focus, and they are in precise focus (three points always fall on one plane). I had to fiddle with the tiny adjustments quite a bit to get them just right. I was trying to avoid too small an f-stop because there was a breeze and those leaves were just dancing. But I wanted all those major tree branches to be sharp. The main subject was pretty close to the camera and thus depth of field was narrow even at a small f-stop.

http://www.rickdenney.com/images/japns_maple_scan0015_lr.jpg
Japanese Maple in Autumn

I positioned the camera so that the leaves at the left edge were in the focus plane.

I bet I spent over half an hour fiddling with the tilt and swing adjustments, using a loupe on the ground glass to check the settings, until my main three points were all perfectly focused. The reward for that effort was an f/16 aperture, and the reward for that was a 1-second shutter speed using Velvia 50. Had I used f/32, I'd have had to find a 4-second period when those leaves were still. Not happening that day.

The lens on this was a 121mm f/8 Super Angulon on 6x12.

In summary: The only time you have to compromise on tilts and swings is if you have subject material you want to be in focus that is not all on the same plane. Then, you have to find a plane that gets close (with "close" having a more demanding definition in the near field) and then stop down to obtain the necessary depth of field. But if you can identify a flat focus plane, then keep adjusting until it's in good focus even wide open.

Rick "the compromise is in deciding where to put the focus plane, not the movements needed to make that focus plane sharply focused" Denney

[Leigh]

There are three planes involved in focusing a view camera. Initially all three are parallel:
one through the film, one through the lensboard, and one through the subject.

The SP enables you to change the plane of focus, that initially went vertically through the subject,
to intersect the other two planes.

Simple description (leaving the back vertical):
Tilting the lensboard forward moves the BOTTOM of the plane of focus toward the camera.

Tilting the lensboard relative to the back DEFINES the plane of focus, which intersects the other two planes at their common line.

For this to work in practice you must consider depth of field (DoF), which varies with the distance from the camera.
Viewed from the side (with from tilt), the region of proper focus looks like a wedge with its apex at the camera,
getting larger as distance increases.

The f-stop controls DoF, but now it's relative to the tilted plane of focus, no longer front-to-back.

- Leigh

[Dennis]

To just do a roughly close adjustment without precises measurements of intersections and such, I look at what I am going to photograph be it table top or landscape in envision how I want the plane of focus to lay and then from experience I know that the plane of focus moves about twice as much as the plane of the lens board. It is a rough estimate but gets you close enough to start fine tuning with the loupe.

[Cletus]

Thank you for the practical advice -

E., I will definitely try the "Map Trick" as an exercise to help me illustrate your point. I do understand there must be three basic planes that must intersect - that being the Film, Lens and Subject planes.

In my example of the camera pointed up at the wall, this was my assumption:

Since the camera is not level (and the wall is), the wall forms the flat, 2D subject plane, with a line extending straight down toward the center of the earth. Tilting the front standard back slightly, so the top of the front standard is further from the wall than the bottom of the front standard - remember the camera is not level, it's pointed up at an angle - forms the lens plane, whose line will eventually converge with the subject plane line. Finally, adding some back tilt to the rear standard, the film plane line will now converge with the other two and come to a "point" somewhere, probably meeting somewhere below ground level, ultimately.

Doesn't this still satisfy the SP requirements? Isn't the actual location of the node of the three converging lines irrelevant? This was the crux of my question I guess. It seems to me, when I've tried to experiment with this, and even though the three planes seem to eventually meet, I am still unable to get my 2D subject plane into sharp focus. There could be other factors affecting this as well and looking at the camera from the side to determine the approximate location of the convergence makes a lot of sense to me. It never occurred to me to do that.

rdenny - Nice photo of the tree and nice way to illustrate your example, BTW.

Anyway - Collectively, you have all confirmed my suspicion that a 2D plane, regardless of it's orientation, should be able to be brought into sharp focus using movements correctly. That whole issue with me is based on some MIS information I received some time ago, when just learning how to manipulate a view camera and it's always bothered me that it didn't sound correct. Also, I do understand that a 3D plane, as opposed to 2D one, will need a certain amount of DoF to compensate for what can't be brought into tack sharp focus.

I plan to refer back to this thread while doing some test shots on the table tomorrow!

[E. von Hoegh]

Just point the camera at the wall, make all three planes parralel, and apply front rise. Scheimpflug isn't for every situation.

[ghostcount]

...
http://www.rickdenney.com/images/japns_maple_scan0015_lr.jpg
Japanese Maple in Autumn
...

Rick, very impressive. Another proof patience has it's rewards. Bravo!

[Leigh]

Since the camera is not level...
Tilting the front standard back slightly
First problem...
You must always start with the tripod and the camera level on both left/right and front/back axes.
You can make adjustments subsequently, but you need a known starting point.

Second problem...
Tilting the lensboard back totally screws up the SP.
It places the line of intersection between the film plane and the lensboard plane ABOVE the camera,
which means that the plane of sharp focus will go through that line, i.e. in empty air.

Standard setup for architecture or other tall subject:
Set the camera and tripod both level.
Focus on the subject.
Use front rise to bring the top of the subject into view.
If the camera rise is insufficient, tilt the entire camera up at the front, using the tripod head, then reset the back vertical. (This is why you don't use a ball head.)

Adjust front tilt as needed to implement SP, bringing desired features (particularly foreground) into focus.
The required lensboard tilt is very slight except in highly unusual circumstances.

HTH

- Leigh

[David Lobato]

First problem...
You must always start with the tripod and the camera level on both left/right and front/back axes.
You can make adjustments subsequently, but you need a known starting point.

Second problem...
Tilting the lensboard back totally screws up the SP.
It places the line of intersection between the film plane and the lensboard plane ABOVE the camera,
which means that the plane of sharp focus will go through that line, i.e. in empty air.

Standard setup for architecture or other tall subject:
Set the camera and tripod both level.
Focus on the subject.
Use front rise to bring the top of the subject into view.
If the camera rise is insufficient, tilt the entire camera up at the front, using the tripod head, then reset the back vertical. (This is why you don't use a ball head.)

Adjust front tilt as needed to implement SP, bringing desired features (particularly foreground) into focus.
The required lensboard tilt is very slight except in highly unusual circumstances.

HTH

- Leigh

I second everything Leigh says; adding, start with the camera at the zero settings on the controls. Do not try to guess an amount of tilt before setting up, or else you risk getting hopelessly confused under the dark cloth. For lenses 150mm and under, tilt in outdoor situations is quite small. Work methodically and thoughtfully on each step of the process, beginning with planting the tripod. This is a prime example of when "a shortcut can be the longest distance between two points". Don't fear making a mistake, simply go back a step or two in the process and try again. Before long, setup will be second nature, and you can concentrate more on light metering and composition.

[Leigh]

I second everything Leigh says; adding, start with the camera at the zero settings on the controls.
Yep. I forgot that. :eek:

- Leigh

[Jim Jones]

When tilting the front standard, one can exceed the coverage of many lenses, leading to unsharpness in an image edge. Unless the lens has more coverage than needed, try to keep the axis of the lens pointed fairly near the center of the ground glass.

[Leigh]

Image circle is a consideration in all situations, even with no movements.

- Leigh

[E. von Hoegh]

A general rule is that front movements eat the image circle at a rapid pace while rear movements do not place any demands upon image circle.

If you have cut corners on your GG, you can peer through the open corners at the lens at working aperture - if you see the whole diaphragm as a clear circle, you're still good. If the opening looks like a cat's pupil, you've gone too far.

[Lon Overacker]

...why doesn't the entire scene, if done correctly, come into perfect, sharp focus on the GG?

Maybe I missed someone's answer already, but it seems to me that the simple answer to this question is being missed. Other than photographing a perfectly flat surface and having everything perfectly lined up in parallel, you will never ever get the entire scene on the GG in exact focus. The only thing exactly in focus is whatever lies in the "plane of focus." Depth of field, tiny apertures is what brings everything else in to "acceptable focus" in front and behind the plane of focus.

I did a write up (http://www.lonoveracker.com/pdf/planeoffocus_v100410.pdf) on this that may help - especially since it has examples where you can visualize it much better than any written explanations can do. I'm not a technical photographer really so some of you gurus might find some things that aren't exactly correct, but I did my best and the intended audience is of course someone new to LF. If anyone takes a look and finds something that needs to be corrected, feel free to drop me a note. tx

Hope this helps.

Lon

[Leigh]

Other than photographing a perfectly flat surface and having everything perfectly lined up in parallel, you will never ever get the entire scene on the GG in exact focus.
Sorry, but that's not true.

You can photograph a ramp and have the entire surface in focus.
You can even have a building at the end, and people on the ramp, all in focus.

This does not depend on extremely small apertures.
It's a simple application of Scheimpflug.

- Leigh

[Lon Overacker]

Leigh, of course - the ramp is a flat surface. That building at the end of the ramp though... the plane of focus will only slice through that building and so technically you can not get the entire building and the ramp in focus on the GG (assuming of course you are focusing wide open.) You also assumed that I meant a flat surface such as a vertical wall. Lot's of examples of flat surfaces, such as the ramp, which of course require the use of Scheimpflug.

Of course I agree that it "does not depend on extremely small apertures," - That works when nearly everything falls on or very near the chosen plane of focus. The moment you have elements that extend beyond the plane of focus you need smaller apertures, varying depending on how far away those elements are from the plane of focus.

I was simply trying to answer the question, which seemed to be one of concept rather than technique. Rick's image shows that he applied the concept of the plane of focus by choosing his subject plane carefully, then used the techniques to achieve the desired plane of focus.

Lon

[Leigh]

That building at the end of the ramp though... the plane of focus will only slice through that building and so technically you can not get the entire building and the ramp in focus on the GG (assuming of course you are focusing wide open.)
Another invalid assumption.

I intentionally did not specify the size of the building, nor its distance from the camera.

You made a blanket statement previously which is simply not correct, to wit that the three surfaces must be parallel in order to achieve focus.
Not true with the ramp example.

- Leigh

[federicomar]

...
I did a write up (http://www.lonoveracker.com/pdf/planeoffocus_v100410.pdf) on this that may help - especially since it has examples where you can visualize it much better than any written explanations can do. I'm not a technical photographer really so some of you gurus might find some things that aren't exactly correct, but I did my best and the intended audience is of course someone new to LF. If anyone takes a look and finds something that needs to be corrected, feel free to drop me a note. tx

Hope this helps.

Lon

thank you for the pdf, much appreciated

[tih]

I really like Harold Merklinger's writings on this subject. See http://www.trenholm.org/hmmerk/ for the complete collection. His books go into more detail than most photographers need, but are very interesting if you're so inclined. For an introduction to Merklinger's approach to practial use of the Scheimpflug principle, I'd recommend his articles in View Camera magazine, available from the above site as http://www.trenholm.org/hmmerk/VCFaDOF1.pdf and http://www.trenholm.org/hmmerk/VCFaDOF2.pdf

-tih

[Tim Meisburger]

Thanks Lon. I enjoyed it as well.

[SergeiR]

or you can also just watch video.. Might spot something here ;)

http://www.youtube.com/watch?v=gR4m70xr9mE

[C. D. Keth]

One useful thing to understand about the scheimpflug principle is the volume of the depth of field as movements are applied. When the movements are zeroed out, the depth of field makes a section of a cone with the smaller circle toward the camera, the larger circle away from camera, and the subject plane somewhere between 1/3 and 1/2 of the way in between. Once you account for the fact that your film is a rectangle and the edges of that circle are cut off, that leaves you with a section of a 4-sided pyramid.

If you apply some front tilt with the top of the lensboard away from the film, that volume that is in focus changes. In fact, it changes pretty dramatically. That 4-sided pyramid shape becomes more like a wedge. The sharp edge of the wedge is at the line where the subject plane, lens plane, and film plane intersect. The wedge then goes off from there with about a third of the volume toward camera from the theoretical subject plane and two thirds beyond it. That means that the scheimpflug principle gives you a way to include more and more stuff in focus at it gets further from the camera. You do this by placing that subject plane carefully. Sometimes, you place that theoretical plane itself in clear air but the volume of depth of field that surrounds it is able to encompass what you need to be sharp.

Take for example the theoretical situation that Leigh posed above in this thread. There's a ramp close to camera leading up to an area with some people, and a building beyond that. If you were to place the subject plane so it hits the closest part of the ramp, perhaps flies over the people's head by 6 feet, and then cuts the building about 2/3 of the way up, you very well might be able to get all that in focus once that plane you're imagining expands into a wedge of focused space.

[ic-racer]

Also, I do understand that a 3D plane, as opposed to 2D one, will need a certain amount of DoF to compensate for what can't be brought into tack sharp focus.



3D plane?? Does not exist. A plane, by definition, only has two dimensions. Maybe that is the source of the misunderstanding?

[Ian David]

you very well might be able to get all that in focus once that plane you're imagining expands into a wedge of focused space.

Except that it is not a wedge of focused space, but rather a wedge of acceptable sharpness. There is still only a single plane of true focus, right?

[C. D. Keth]

Except that it is not a wedge of focused space, but rather a wedge of acceptable sharpness. There is still only a single plane of true focus, right?

That's technically correct but it's much easier to explain it as focused space and unfocused space.

[rdenney]

That's technically correct but it's much easier to explain it as focused space and unfocused space.

Ian's question reveals the troubles of attempting a precise explanation without being careful about all the terms. Much pain and suffering on this forum has resulted from the lack of clarity (so to speak) between "in focus" and "acceptably sharp". (You could have said "apparent focus", which addresses a lot of issues.)

But then it's sort of a sport on this forum to out-precise the next guy.

Rick "guilty of that as anyone" Denney

[Cletus]

Lon - nice article! Nice illustrations! That's going in my bookmarks and my reading list. I'm just now checking back on this discussion (that I started, I'm afraid) and yours is a comprehensive and accessible explanation. Not that others explanations have been lacking, either.

I guess what prompted the question in the first place - not to get this all started again! - was the fact that to me, ANY TIME you have ~some front forward tilt and ~some back rear tilt, you have met the conditions of the Sheimpflug Principle I that lens plane, film plane and ostensibly subject plane will converge to a point. Period. That does NOT determine exactly WHERE the plane of best focus will land, but it does meet the requirements of the SP.

That was really my only point in the first place. If you happen to be focussing on a "flat" plane, whatever the orientation, it should be in sharp focus in its entirety and need not stop to f128 to get there.

[Cletus]

Oh boy. I should've kept my mouth, or fingers, shut! I get it, I was just reiterating with that last. Please disregard my comments!

[Leonard Evens]

The Scheimpflug Principle states that the subject plane, the lens plane, and the image plane intersect in a common line. So if the lens plane and plane of the gg are tilted with respect to one another, thus intersecting in a line, the subject plane must pass through that line. But the Scheimplug principle doesn't tell which of the infinitely many planes also passing through that line is the subject plane. It just must be one of them. Of course, you can see the subject plane simply by looking at your gg. It is what is in exact focus.

If what you see in focus on your gg is not your desired subject pane, you may try remedy that by focussing, i.e., by moving either the front standar or or the rear standard parallel to itself along the rail. That will of course move the line of intersection of the lens plane and image plane as well as moving the subject plane. If you chose the tilt properly, then at a certain point you desired subject plane will come into exact focus. If you did not choose the tilt properly, that won't ever happen. Thus you must change the tilt.

Here is what I do. I find it better to focus by moving the rear standard. I start by making a guess and tilting the front standard about 5 degrees. I choose two points, a near point and a far point, which I want to be in my desired subject plane. I focus by moving the rear standard until the far point is in focus. I then refocus with the rear standard to bring the near point into focus. If that requires me to move the standards further apart, I increase the tilt. If that requires me to move the standards closer together, I decrease the tilt. After two or three iterations of this process, I find both near and far point in focus, and of course my desired subject plane is in focus.

In doing this, you can be confused by depth of field since that my confuse you about where the exact focus is. You should always focus wide open and use a loupe to try to reduce the amount of depth of field so you can identify where the exact focus is.


It is also important to know what the depth of field region looks like after a tilt. It forms a "wedge" shaped region extending from a base line, below the lens, called the hinge line. the plane of exact focus cuts that region in two in that any vertical plane is cut by the region into two equal planar regions, one above the subject plane and one below. The position of the hinge line is determine by the tilt. As you increase the tilt of the lens plane, it moves closer to the lens but never gets closer to the lens than one focal length. With the tilt fixed, if you focus by moving the rear standard, the whole wedge swings about the hinge line, with the subject plane moving but always centered in the wedge as described above.

[Leigh]

...lens plane, film plane and ostensibly subject plane will converge to a point. Period. That does NOT determine exactly WHERE the plane of best focus will land, but it does meet the requirements of the SP.
You can only control two planes: the lens plane (normal to the lens optical axis), and the film plane.

Those two planes intersect in a line (provided they're not parallel to each other).
A plane drawn through that line and intersecting the subject at the point of focus defines the plane of focus. You cannot change it.

- Leigh

[Cletus]

Leigh -

Yes, I understand. I should have limited any further commentary and "reiterations" to avoid dragging this into redundancy. I read (and re-read) many of yours and others comments and it's very clear to me now. I even some test setups on a table to demonstrate to myself some of these principles. IOW - I practiced a bit!

Thank you for sharing your views and considerable knowledge regarding this rather complicated (I guess it can be as complicated as we want, yes?) subject.

Cletus

[Leigh]

Hi Cletus,

One of the problems with this and many other concepts is that explaining them in writing is much more cumbersome
than demonstrating the principle in person, or with a video or some similar visual medium.

Good luck, and good shooting.

- Leigh